The present invention relates to a method for assembling an electrochemical cell and, more particularly, to a method for assembling a primary electrochemical cell of a cylindrical design and including a stacked array of cell components.
Primary electrochemical cells are utilized for a wide variety of applications and are commonly available in a large assortment of sizes and shapes. One well known type of primary electrochemical cell is a so-called cylindrical cell. A particularly suitable design for such a cell, especially for high rate (greater than 1 mA/cm.sup.2) and low-temperature (to -40.degree. C.) applications, is described in the aforementioned co-pending application Ser. No. 159,271. The cell described in the co-pending application includes a battery stack disposed within a metal housing of the cell together with an electrolytic solution. The battery stack comprises a large number of thin, generally circular, annular-shaped components. These components are superimposed on each other in a vertical stacked array relative to the housing and relative to a central, elongated, cylindrical, metal terminal member which extends completely through the battery stack and is encircled by the battery stack components.
The components of the battery stack include a plurality of anode structures and a plurality of carbon current collector electrode/separator assemblies arranged in the array in alternation with the anode structures. The elongated metal terminal member may be a solid rod or, in the case of a cell of large physical size, a perforated hollow tube for increasing exposure of the stack to electrolytic solution. Each of the anode structures includes a thin metal disc, for example, of lithium, and a contact member adjacent to a central opening in the disc. The contact member has a central opening aligned with the opening in the disc and a plurality of resilient portions defined by said central opening by which the anode structure can be forced onto the end of, and along, the central terminal member to its required position in the stack. When in position, the resilient portions of the contact member grip onto the central terminal member to make direct physical and electrical contact therewith. Each of the carbon current collector electrode/separator assemblies as employed in the abovedescribed cell includes a pair of thin carbon/fiberglass cathode structures physically adjacent to opposite sides of a thin metal (e.g., nickel) current collector disc. These latter components have central openings of a size to space, or electrically isolate, the components from the central terminal member. The current collector disc is of a size and configuration so as to make direct physical and electrical contact with the interior wall of the housing of the cell.
The electrochemical cell as described hereinabove may be assembled by first assembling the entire battery stack relative to the central terminal member outside of the housing and then placing the entire battery stack into the housing or, alternatively, by assembling the components of the battery stack one by one relative to the central terminal member within the housing of the cell. While either assembly method produces generally satisfactory results, it is possible as the battery stack is built up for one or more of the cell components, especially the anode structures which are secured to the central terminal member at the centers thereof, to flare up at the outer edges. This flaring up of the outer edges of the anode structures is due to the fact that the anode structures themselves are very thin and lightweight, as are the other components on opposite sides of the anode structures, as a result of which insufficient compressive forces exist at the outer edges of the anode structures to keep them in a flat position. This flaring up of the outer edges of the anode structures tends to increase in a direction from the bottom of the stack to the top of the stack. As a result, the overall battery stack may be less flat and compact than required, and undesirable gaps or spaces may exist between various ones of the components, leading to the possibility of breakage of one or more of these components.